1. Field of the Invention
The present invention relates to a method for fixing a device to a wall, and to a corresponding tank.
The invention relates notably to a method for fixing a device to the internal surface of a wall of a duct or of a for tank cryogenic fluid and in particular of a tank intended to contain liquid oxygen.
The invention may relate more particularly to a bonding-based fixing system for mounting devices inside a cryogenic tank containing or being able to contain liquid oxygen or air. Such a tank may, for example, form part of a space launcher or of any other liquid oxygen storage or transportation system. The device to be fixed in the tank may be, for example, one or more measuring devices (such as temperature or level probes, etc.), piping, deflectors or any other device for monitoring or measuring the displacement of the fluids inside the tank.
The invention can in particular be used for the mounting, in a tank, of a deflecting wall such as that described in the documents FR2919852 or FR2941678.
The invention may also be applied to devices mounted on any system that may be exposed to liquid oxygen or air, such as ducts for cryogenic fluids.
2. Related Art
Techniques are known for fixing to the walls of cryogenic containers and ducts by mechanical fastening, by welding/brazing and by bonding. Depending on the geometry of the wall, the fixing by mechanical fastening may require modifications of said wall (for example, drilling of holes, added support, etc.) and an impairment of its properties such as the seal-tightness, mechanical strength or weight. Fixing by welding is applicable only to certain pairings of materials and often requires a modification of the geometry of the wall, especially if the latter is of small thickness. The high temperatures that are required may result in an impairment of the properties of the materials. Fixing by bonding is generally more versatile than the preceding techniques. It can be used to couple a large number of homogeneous or heterogeneous materials and its application is relatively simple. It does not require any modification of the geometry of the wall.
Now, the constraints associated with the embrittlement of the materials at low temperature and with the differential thermal contraction between the bond and the materials to be bonded make the selection of a bond particularly critical for cryogenic applications. Some bonds, in particular certain epoxies, silicones and urethanes, are known for their applications in cryogenics. However, these bonds are not chemically compatible with powerful oxidizers such as liquid oxygen, which results in a significant risk of combustion when additional energy is applied such as a mechanical impact or an electrostatic discharge.
Most of the plastic materials and adhesives used for mounting devices in tanks pose safety problems because these materials are liable to generate a fire when they are exposed to a powerful oxidizer such as liquid oxygen. Bonding the devices inside a liquid oxygen tank requires a rigorous selection of the materials used and of the mounting structure.